I think Charlotte had been putting too much pressure on herself to be a professional rider and do 10 other things at the same time. Now that she has decided to make it a hobby, she is relaxing and enjoying herself.

Yes, i agree. Maybe she doesn't feel like "i have to make it because it is my job!" She is surely more relaxed. Even if she does a mistake, it is just a hobby now, she is not a professional rider to care about every single detail of professionalism.

Maybe at some point in the past she would have liked to turn pro, if the results had been a tiny bit better?
Otherwise the title of this thread is basically wrong...

I think the title is fine. Really, there are many more amateur equestrians than professionals, who actually earn their living buying and selling horses more than winnings from competitions. Often times the very best horses are sold to very wealthy amateurs. For example last month Jessica Springsteen (daughter of Bruce) won the American Gold Cup in NY. Georgina Bloomberg (daughter of Michael) is another example.